To meet requirements for increase in electric power demand, and downsizing and high reliability of electric power equipment, there is a remarkable tendency that a gas insulated switchgear (hereinbelow, referred to as a “GIS”) in which a tank charged with sulfur hexafluoride gas (SF6) having high insulation and breaking performance accommodates electric devices such as an energization conductor and a breaking unit, to attain significant size reduction of the entire switchgear, is a main stream as a recent electric switchgear.
The most important constituent element of the GIS is the breaking unit (hereinbelow, referred to as a “GCB”). The GCB has a structure where the breaking unit is supported via an insulting spacer or an insulating tube in the breaking unit tank charged with the SF6 gas.
This breaking unit quickly breaks not only a general load current but a short circuit current upon accident. At this time, arc-extinguishing gas the temperature of which has become high by arc overheating (hereinbelow, referred to as “high-temperature gas”) flows from the exhaust conductor to the tank side, to lower the peripheral insulation performance, and cause ground fault.
As conventional art, one is known in which cooling blades are provided inside an exhaust tube such that high-temperature gas is applied to the cooling blades, to promote stirring of the peripheral low-temperature gas and quickly cool down the temperature of the gas discharged from an exhaust hole, as disclosed in Patent Literature 1.
However, downsizing of the recent GCB is advanced and downsizing of the breaking unit itself is also advanced. The downsizing of the breaking unit is accompanied by downsizing of the exhaust conductor on the fixed side or movable side, or both sides, in many cases. In this situation, it is difficult to provide the cooling blades as described above in the exhaust tube in view of balancing assembling property and arrangement space.
Further, the exhaust hole provided in the exhaust conductor is also used as an assembling hole for connection of a link mechanism of the breaking unit upon assembly. It is necessary that the exhaust hole has a sufficient size for assembly. When the downsizing of the breaking unit is advanced, the size of the exhaust hole is too large with respect to the ratio of the entire breaking unit.
On the other hand, when the exhaust hole is significantly reduced, a problem of reduction of the breaking performance or the like occurs. Further, when the high-temperature gas is discharged from a small exhaust hole, the end of the exhaust hole is likely to be exposed to the high-temperature gas, making it impossible to avoid the degradation of insulation performance.
Even though the breaking unit is downsized, it does not directly affect the reduction of the high-temperature gas caused upon arc extinguishing, but rather the space for cooling the high-temperature gas is reduced. There are many problems in setting of the exhaust hole. When it is not possible to set an appropriate exhaust hole, the degradation of insulation performance between the exhaust conductor and the ground tank becomes a serious problem.